1. Field of the Invention
This invention relates to a magnetic spacing control method for a magnetic head, a read/write circuit, and a magnetic disk device which uses the read/write circuit, to control the magnetic spacing of the magnetic head with respect to the magnetic disk and improve the write characteristics, and in particular relates to a magnetic spacing control method for a magnetic head, a read/write circuit, and a magnetic disk device which uses the read/write circuit, in which, by providing a heat-generating element on the magnetic head, and through heat generation of the heat-generating element, a portion of the magnetic head is caused to protrude, to control the magnetic spacing.
2. Description of the Related Art
With the increasing sophistication of information processing in recent years, data reliability has come to be of vital importance. In magnetic recording/reproduction devices in particular, the ability to record data on the media is the most important function. A magnetic disk device stores magnetic data on magnetic recording media according to reversals of a write current generated from data. This data is read by a read head (in particular, by an MR head using the magnetoresistive effect), by converting magnetic data into electrical signal data, which is sent to a controller.
When a magnetic disk device enters write operation, first the read channel enters write mode by means of a write gate signal from the controller, and flows a write current, which depends on data, to the write head. As shown in FIG. 14, at low temperature and similar, this write head is at low temperature prior to writing, and when writing is begun the application of the write current causes the temperature to rise. This results in transient thermal stress on the magnetic poles of the write head, and as a result thermal expansion of the write poles occurs, and the write poles protrude in the media direction. This is generally called PTP (Pole Tip Protrusion).
As one phenomenon occurring at this time, at the beginning of writing there is no protrusion of poles, and the poles gradually come to protrude in keeping with the time of application of the write current; hence the magnetic spacing of a magnetic head comprising a write head and a read head is comparatively large at the beginning of writing, and the magnetic spacing decreases as writing proceeds.
For this reason, at the beginning of writing the writing ability is reduced compared with at the end of writing. This appears as degradation of the overwrite performance. As shown in FIG. 15, the closer to the beginning of writing (the first writing), the poorer is the ability to overwrite data previously written to the track, and during reading, the previous data appears as noise, so that the error rate is worsened as a result. As the write head gradually protrudes, the magnetic head approaches the media and writing is performed, so that there is a general tendency for overwriting to improve. Particularly when the magnetic disk device is used in a low-temperature environment, the temperature difference between the beginning of writing and the end of writing is large, and the first writing performance is dramatically diminished.
Further, with the rising track densities and recording densities of recent years, lower magnetic spacing for magnetic heads has become imperative (for example, spacings of order 10 nanometers have been sought). For this reason, it is become difficult to maintain a constant magnetic spacing between the magnetic recording media and the magnetic head element. For example, the magnetic head utilizes the wind pressure generated by rotation of the magnetic disk to fly above the disk surface, and so such ambient conditions as the elevation (air pressure) and temperature can cause changes in magnetic spacing, resulting in scattering in the magnetic spacing. Further, scattering among heads, cylinder positions, write current settings, and other factors can also give rise to scattering in the magnetic spacing. These factors may cause declines in write performance and drops in signal quality at times, and at times may cause such problems as element degradation, and in the worst case element destruction and similar, due to contact with the media.
In order to improve the overwrite characteristic, a method has been proposed in which the write current is increased for a fixed length of time from the start of writing, in order to improve overwriting (for example, Japanese Patent Laid-open No. 2004-281012, U.S. Pat. No. 6,798,598). This method only hastens the time for head protrusion immediately after the start of writing, but due to constraints imposed by the maximum value of the write current and the maximum allowable current of the write element, it is difficult to alleviate error rate degradation due to insufficient overwriting in the first sector.
Moreover, another prior method has been proposed in which a heater is provided within the magnetic head, and the amount of protrusion of the magnetic head is controlled through heat generation by the heater (for example, Japanese Patent Laid-open No. 5-020635).
Further, in other prior art, a method has been proposed in which a heater is provided within the magnetic head, and the heater is used to apply heating power when adjustment of the magnetic spacing is necessary, such as for example immediately before writing, and the heating power is increased temporarily to shorten the protrusion response time (for example, Japanese Patent Laid-open No. 2004-342151 (FIG. 7), U.S. Unexamined Patent No. 2005/0057841 (FIG. 7)).
However, when using the first technology of the prior art, the same heating power is applied for both reading and writing in order to adjust the magnetic spacing, and if an acoustic sensor provided in the head is used to detect heat contact, then control is executed to reduce the heating power, and protrusion due to the write current in the write element described above causes the head to make contact with the media. As a result, degradation of and damage to the head tends to occur.
When using the second technology of the prior art, the heater power is increased temporarily when there is a need to adjust the magnetic spacing, and no consideration is given to measures to counter the ambient conditions of wind pressure, temperature, or air pressure, or scattering among heads. Consequently when there are changes in ambient conditions or scattering in head parameters (and in particular among write elements), alleviation of overwrite degradation cannot be expected.